1. Field of the Invention
The invention relates to a fan assembly, more particularly to a heat dissipating fan assembly that can be powered by either a DC power source or an AC power source.
2. Description of the Related Art
A conventional heat dissipating fan is powered using an alternating current (AC) or a direct current (DC) power source. In the AC-powered fan, changes in the magnetic field of an induction coil as a result of a sinusoidal voltage results in rotation of a fan blade unit that is provided with a magnetic element, thereby producing air current to dissipate heat.
The DC-powered fan functions substantially similar to the AC-powered fan. However, in the DC-powered fan, a direct voltage is applied to actuate a Hall element in the DC-powered fan so as to produce the changes in the magnetic field of the induction coil.
Under the circumstances where the dimension and the rotational speed of the AC- and DC-powered fans are the same, the structure of the induction coil in the AC-powered fan is usually larger than that in the DC-powered fan, and the fan blades are made correspondingly smaller, so that the wind pressure and the wind flow of the AC-powered fan are inferior to those of the DC-powered fan. Furthermore, since the induction coil in the AC-powered fan easily produces high temperatures, an aluminum frame is usually used to assist in dissipating the heat of the fan blade unit. However, this only makes the weight of the AC-powered fan heavier. Moreover, since the AC-powered fan produces a stronger electromagnetic wave interference during rotation, it is not suitable for use in high precision instruments.
As compared to the AC-powered fan, the structure of the induction coil in the DC-powered fan is smaller, and the fan blades are made correspondingly larger. As such, the wind pressure and the wind flow of the DC-powered fan are superior. Furthermore, the electromagnetic wave interference and the self-produced heat of the DC-powered fan are smaller such that the DC-powered fan has wider applications. The rotational speed of the DC-powered fan is also easy to control. Moreover, an outer casing of the DC-powered fan can be made of a transparent material, so that when used with a light emitting diode, the appearance of the heat dissipating fan can be enhanced.
However, the conventional DC-powered fan cannot be used where a direct current power source is not available. To resolve this problem, a DC power supply or an AC-to-DC converter has to be separately purchased and installed, which results in added costs.